The present invention relates to a UV-protected electrochromic solution, to its use in an electrochromic device and to an electrochromic device comprising this solution.
Electrochromic devices comprising an electrochromic system are already known.
The electrochromic system of such devices customarily includes pairs of redox substancesxe2x80x94redox couplesxe2x80x94dissolved in an inert solvent. Additionally, conductive salts, light stabilizers and substances which influence the viscosity may be present.
The redox couple used comprises one reducible and one oxidizable substance each. Both are colourless or have only a weak coloration. Under the influence of an electrical voltage the one substance is reduced and the other oxidized, with at least one becoming coloured in the process. After the voltage is switched off, the two original redox substances are formed once more, which is accompanied by the disappearance or fading of the colour. 
U.S. Pat. No. 4,902,108 discloses that suitable such redox couples are those in which the reducible substance has at least two chemically reversible reduction waves in the cyclic voltammogram and the oxidizable substance, correspondingly, has at least two chemically reversible oxidation waves.
Electrochromic devices can find multifarious applications. For example, they may take the form of a car rearview mirror which when travelling at night can be darkened by applying a voltage, thus preventing the driver being dazzled by headlights of other vehicles (cf. e.g. U.S. Pat. Nos. 3,280,701, 4,902,108, EP-A-0 435 689). Such devices may also be employed in window panes or car sun-roofs where, following the application of a voltage, they provide shade from the sunlight. Finally, it is possible to use such devices to construct a display device for the graphic representation of information in the form of letters, numbers and symbols.
Electrochromic devices normally consist of a pair of glass or plastic plates, one being mirrored in the case of a car mirror. One side of these plates is coated with a transparent, electroconductive layer, e.g. indium tin oxide (ITO). These plates are then used to construct a cell; to this end their facing, electroconductively coated side is attached, preferably by means of adhesive bonding, to an annular or rectangular sealing ring. The sealing ring establishes a uniform distance between the plates of, for example, from 0.1 to 0.5 mm. This cell is then filled, via an aperture, with an electrochromic solution and then tightly sealed. By way of the ITO layer it is possible to contact the two plates separately.
The electrochromic systems known from the prior art comprise redox couples which following the reduction and oxidation, respectively, form coloured free radicals, cationic free radicals or anionic free radicals that are chemically reactive. As known, for example, from Topics in Current Chemistry, Vol. 92, pp. 1-44 (1980) such (ionic) free radicals may be sensitive to electrophiles or nucleophiles or else to free radicals. In order, therefore, to achieve a high level of stability in an electrochromic device comprising an electrochromic system of this kindxe2x80x94a system which is intended to withstand several thousand switching cyclesxe2x80x94it is necessary to ensure that the solvent used is absolutely free from electrophiles, e.g. protons, nucleophiles and oxygen. It must also be ensured that such reactive species are not formed by electrochemical processes taking place at the electrodes during operation of the electrochromic device.
The back-reaction to RED1 and OX2 that is formulated in the above equation also takes place continuously away from the electrodes within the volume of the solution while the electrochromic device is in operation. Owing to the above-described hazards of degradation reactions of the (ionic) free radicals by electrophiles, nucleophiles or free radicals it is important, for the long-term stability of the display, that the back-reaction in accordance with the above equation is able to take place as rapidly as possible and without side reactions.
Electrochromic devices of this kind generally exhibit sensitivity to light, especially UV light. Consequently, electrochromic devices have been disclosed which comprise UV stabilizers, for example in U.S. Pat. No. 5,280,380.
It has now been found that by coupling RED1 and OX2 by way of a covalent chemical bond the electron transfer is facilitated and thus the back-reaction indicated in the above equation can be accelerated and side reactions avoided.
It has likewise been found that electrochromic solutions comprising such RED1 and OX2 bridged via a covalent chemical bond can be effectively protected by particular UV absorbers against destruction by UV light.
The present invention accordingly relates to an electrochromic solution comprising at least one oxidizable substance RED1 which releases electrons at an anode, and at least one reducible substance OX2 which accepts electrons at a cathode and in so doing undergo transition from a weakly coloured or colourless form into a coloured form OX1 and RED2, respectively, accompanied by an increase in the absorbance in the visible region of the spectrum, the weakly coloured or colourless form being restored after charge equalization, characterized in that at least one of the substances RED1 and OX2 that are present are linked covalently to one another via a bridge and in that there is at least one UV absorber selected from the classes of the unsubstituted and substituted cinnamic esters and of the unsubstituted and substituted 2-hydroxybenzophenones. At least one of the oxidation- or reduction-induced transitions RED1≈OX1 or OX2≈RED2, respectively, is associated with an increase in the absorbance in the visible region of the spectrum.
The reduction and oxidation processes in the electrochromic system of the invention generally take place by electrons being accepted or released at a cathode or anode, respectively, a potential difference of from 0.3 to 3 V preferably obtaining between the electrodes. After the electrical potential has been switched off, charge equalization takes placexe2x80x94in general spontaneouslyxe2x80x94between the substances RED2 and OX1, accompanied by disappearance or fading of the colour. Such charge equalization also takes place even while the current is flowing in the interior of the electrolyte volume.
The electrochromic solution of the invention preferably comprises at least one electrochromic substance of the formula (I)
Y"Brketopenst""Parenopenst"Bxe2x80x94Z"Parenclosest"a"Parenopenst"Bxe2x80x94Y"Parenclosest"b"Brketclosest"cBxe2x80x94Zxe2x80x83xe2x80x83(I),
in which
Y and Z independently of one another represent a radical OX2 or RED1, subject to the proviso that at least one Y represents OX2 and at least one Z represents RED1,
where
OX2 represents the radical of a reversibly electrochemically reducible redox system, and
RED1 represents the radical of a reversibly electrochemically oxidizable redox system,
B represents a bridge
c represents an integer from 0 to 5, and
a and b independently of one another represent an integer from 0 to 5, preferably an integer from 0 to 3,
and at least one UV absorber selected from the classes of the unsubstituted and substituted cinnamic esters and of the unsubstituted and substituted 2-hydroxybenzophenones.
The electrochromic solution preferably comprises at least one electrochromic substance of the formula (I) in which
Y represents OX2 and Z represents RED1 and Y and Z alternate in their sequence.
With particular preference, the electrochromic system of the invention comprises at least one electrochromic substance of the formula
OX2xe2x80x94Bxe2x80x94RED1xe2x80x83xe2x80x83(Ia),
OX2xe2x80x94Bxe2x80x94RED1xe2x80x94Bxe2x80x94OX2xe2x80x83xe2x80x83(Ib),
RED1xe2x80x94Bxe2x80x94OX2xe2x80x94Bxe2x80x94RED1xe2x80x83xe2x80x83(Ic),
or
OX2xe2x80x94(Bxe2x80x94RED1xe2x80x94Bxe2x80x94OX2)dxe2x80x94Bxe2x80x94RED1xe2x80x83xe2x80x83(Id),
in which
OX2, RED1 and B have the meaning indicated above and
d represents an integer from 1 to 5,
and at least one UV absorber selected from the classes of the unsubstituted and substituted cinnamic esters and of the unsubstituted and substituted 2-hydroxybenzophenones.
With very particular preference, the electrochromic solution of the invention comprises at least one electrochromic substance of the formulae (Ia)-(Id)
in which
OX2 represents the radical of a cathodically reducible substance which in its cyclic voltammogram, recorded in an inert solvent at room temperature, exhibits at least two chemically reversible reduction waves, the first of these reduction waves leading to an increase in the absorbance at at least one wavelength in the visible region of the electromagnetic spectrum,
RED1 represents the radical of an anodically reversibly oxidizable substance which in its cyclic voltammogram, recorded in an inert solvent at room temperature, exhibits at least two chemically reversible oxidation waves, the first of these oxidation waves leading to an increase in the absorbance at at least one wavelength in the visible region of the electromagnetic spectrum, and
B represents a bridge,
and at least one UV absorber selected from the classes of the unsubstituted and substituted cinnamic esters, preferably of the unsubstituted and substituted 3,3-diphenylacrylic esters and of the unsubstituted and substituted 2-cyano-3,3-diphenylacrylic esters, and from the class of the unsubstituted and substituted 2-hydroxybenzophenones.
Particular preference is given to an electrochromic solution of the invention which comprises at least one substance of the formula (Ia)-(Id) in which
OX2 represents a radical of the formulae 
xe2x80x83where
R2 to R5, R8, R9, R16 to R19 independently of one another denote C1- to C18-alkyl, C2- to C12-alkenyl, C3- to C7-cycloalkyl, C7- to C15-aralkyl or C6- to C10-aryl, or
R4 and R5 or R8 and R9 together form a xe2x80x94(CH2)2xe2x80x94 or xe2x80x94(CH2)3xe2x80x94 bridge,
R6, R7 and R22 to R25 independently of one another denote hydrogen, C1- to C4-alkyl, C1- to C4-alkoxy, halogen, cyano, nitro or C1- to C4-alkoxycarbonyl, or
R22 and R23 and/or R24 and R25 form a xe2x80x94CHxe2x95x90CHxe2x80x94CHxe2x95x90CHxe2x80x94 bridge,
R10 and R11; R12 and R13; R14 and R15 independently of one another denote hydrogen or in pairs denote a xe2x80x94(CH2)2xe2x80x94, xe2x80x94(CH2)3xe2x80x94 or xe2x80x94CHxe2x95x90CHxe2x80x94 bridge,
R20 and R21 independently of one another denote O, Nxe2x80x94CN, C(CN)2 or Nxe2x80x94C6xe2x80x94 to C10-aryl,
R26 denotes hydrogen, C1- to C4-alkyl, C1- to C4-alkoxy, halogen, cyano, nitro, C1- to C4-alkoxycarbonyl or C6- to C10-aryl,
R69 to R74 independently of one another denote hydrogen or C1-C6-alkyl, or
R69; R12 and/or R70; R13 form a xe2x80x94CHxe2x95x90CHxe2x80x94CHxe2x95x90CHxe2x80x94 bridge,
E1 and E2 independently of one another denote O, S, NR1 or C(CH3)2, or
E1 and E2 together form an xe2x80x94Nxe2x80x94(CH2)2xe2x80x94Nxe2x80x94 bridge,
R1 denotes C1- to C18-alkyl, C2- to C12-alkenyl, C4- to C7-cycloalkyl, C7- to C15-aralkyl, C6- to C10-aryl,
Z1 denotes a direct bond, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94C(CH3)xe2x95x90CHxe2x80x94, xe2x80x94C(CN)xe2x95x90CHxe2x80x94, xe2x80x94CClxe2x95x90CClxe2x80x94, xe2x80x94C(OH)xe2x95x90CHxe2x80x94, xe2x80x94CClxe2x95x90CHxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94, xe2x80x94CHxe2x95x90Nxe2x80x94Nxe2x95x90CHxe2x80x94, xe2x80x94C(CH3)xe2x95x90Nxe2x80x94Nxe2x95x90C(CH3)xe2x80x94 or xe2x80x94CClxe2x95x90Nxe2x80x94Nxe2x95x90CClxe2x80x94,
Z2 denotes xe2x80x94(CH2)rxe2x80x94 or xe2x80x94CH2xe2x80x94C6H4xe2x80x94CH2xe2x80x94,
r denotes an integer from 1 to 10,
Xxe2x88x92 denotes an anion which is redox-inert under the conditions,
where the bond to the bridge B is via one of the radicals R2-R19, R22-R27 or, if E1 or E2 represents NR1, is via R1, and the radicals mentioned in that case represent a direct bond,
RED1 represents one of the following radicals 
xe2x80x83in which
R28 to R31, R34, R35, R38, R39, R46, R53 and R54 independently of one another denote C1- to C18-alkyl, C2- to C12-alkenyl, C3- to C7-cycloalkyl, C7- to C15-aralkyl or C6- to C10-aryl, and R46, R53 and R54additionally denote hydrogen,
R32, R33, R36, R37, R40, R41, R42 to R45, R47, R48, R49 to R52 and R55 to R57 independently of one another denote hydrogen, C1- to C4-alkyl, C1- to C4-alkoxy, halogen, cyano, nitro, C1- to C4-alkoxycarbonyl or C6- to C10-aryl and R57 and R58 additionally denote an optionally benzo-fused aromatic or quasiaromatic five- or six-membered heterocyclic ring and R48 additionally denotes NR75R76,
R49 and R50 and/or R51 and R52 form a xe2x80x94(CH2)3xe2x80x94, xe2x80x94(CH2)4xe2x80x94, xe2x80x94(CH2)5xe2x80x94 or xe2x80x94CHxe2x95x90CHxe2x80x94CHxe2x95x90CHxe2x80x94 bridge,
Z3 denotes a direct bond, a xe2x80x94CHxe2x95x90CHxe2x80x94 or xe2x80x94Nxe2x95x90Nxe2x80x94 bridge,
xe2x95x90Z4xe2x95x90 denotes a direct double bond, a xe2x95x90CHxe2x80x94CHxe2x95x90 or xe2x95x90Nxe2x80x94Nxe2x95x90 bridge,
E3 to E5, E10 and E11 independently of one another denote O, S, NR59 or C(CH3)2, and E5 additionally denotes Cxe2x95x90O or SO2, or
E3 and E4 independently of one another denote xe2x80x94CHxe2x95x90CHxe2x80x94,
E6 to E9 independently of one another denote S, Se or NR59,
R59, R75 and R76 independently of one another denote C1- to C12-alkyl, C2- to C8-alkenyl, C3- to C7-cycloalkyl, C7- to C15-aralkyl or C6- to C10-aryl, and R75 additionally denotes hydrogen, or
R75 and R76 in the definition of NR75R76 form, together with the N atom to which they are attached, a five- or six-membered, saturated ring which can contain further heteroatoms,
R61 to R68 independently of one another denote hydrogen, C1- to C6-alkyl, C1- to C4-alkoxy, cyano, C1- to C4-alkoxycarbonyl or C6- to C10-aryl, or
R61 to R62 and R67; R68 independently of one another, together form a xe2x80x94(CH)2)3xe2x80x94, xe2x80x94(CH2)4xe2x80x94 or xe2x80x94CHxe2x95x90CHxe2x80x94CHxe2x95x90CHxe2x80x94 bridge,
v denotes an integer between 0 and 10,
the bond to the bridge B being via one of the radicals R28-R58, R61, R62, R67, R68 or, if one of the radicals E3-E11 represents NR59, is via R59 and the above-mentioned radicals in that case represent a direct bond, and
B represents a bridge of the formula xe2x80x94(CH2)nxe2x80x94 or xe2x80x94[Y1s(CH2)mxe2x80x94Y2]oxe2x80x94(CH2)pxe2x80x94Y3qxe2x80x94, each of which is unsubstituted or substituted by C1- to C4-alkoxy, halogen or phenyl,
Y1 to Y3 independently of one another represent O, S, NR60, COO, CONH, NHCONH, cyclopentanediyl, cyclohexanediyl, phenylene or naphthylene,
R60 denotes C1- to C6-alkyl, C2- to C6-alkenyl, C4- to C7-cycloalkyl, C7- to C15-aralkyl or C6- to C10-aryl,
n denotes an integer from 1 to 12,
m and p independently of one another denote an integer from 0 to 8,
o denotes an integer from 0 to 6, and
q and s independently of one another denote 0 or 1,
and comprises at least one UV absorber selected from the formulae 
in which
R101 represents linear or branched C1- to C20-alkyl,
R102 represents hydrogen, cyano or COOR1,
R103, R104 and R106 independently of one another represent hydrogen, C1- to C12-alkyl or C1- to C12-alkoxy,
R105 represents hydrogen, C1- to C12-alkyl, C1- to C12-alkoxy or hydroxyl,
R107 represents hydrogen or C1- to C12-alkyl,
R108 represents hydrogen or
R107 together with R108 represent a C2- or C3-bridge, which is unsubstituted or substituted by up to 3 C1- to C4-alkyl, and
n and m independently of one another represent an integer between 1 and 3.
Very particular preference is given to an electrochromic solution of the invention which comprises at least one substance of the formula (Ia)-(Id)
in which
OX2 represents a radical of the formula (II), (III), (IV) or (V)
where
R2, R3, R4, R5, R8 and R9 independently of one another represent C1- to C12-alkyl, C2- to C8-alkenyl, C5- to C7-cycloalkyl, C7- to C15-aralkyl or C6- to C10-aryl,
R6 and R7 independently of one another represent hydrogen, methyl, ethyl, methoxy, ethoxy, fluoro, chloro, bromo, cyano, nitro, methoxycarbonyl or ethoxycarbonyl,
R10, R11; R12, R13 and R14, R15 independently of one another represent hydrogen or, if Z1 denotes a direct bond, in each case together represent a xe2x80x94(CH2)2xe2x80x94, xe2x80x94(CH2)3xe2x80x94 or xe2x80x94CHxe2x95x90CHxe2x80x94 bridge,
xe2x80x83or
R4, R5 and R8, R9 independently of one another in pairs together represent a xe2x80x94(CH2)2xe2x80x94 or xe2x80x94(CH2)3xe2x80x94 bridge if Z1 denotes a direct bond,
R69 to R74 independently of one another denote hydrogen or C1-C4-alkyl,
E1 and E2 are identical and represent O, S, NR1 or C(CH3)2 or together form an xe2x80x94Nxe2x80x94(CH2)2xe2x80x94Nxe2x80x94 bridge,
R1 represents C1- to C12-alkyl, C2- to C4-alkenyl, C5- to C7-cycloalkyl, C7- to C15-aralkyl or C6- to C10-aryl,
Z1 represents a direct bond, xe2x80x94CHxe2x95x90CHxe2x80x94, C(CH3)xe2x95x90CHxe2x80x94, xe2x80x94C(CN)xe2x95x90CHxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94 or xe2x80x94CHxe2x95x90Nxe2x80x94Nxe2x95x90CHxe2x80x94,
Z2 represents xe2x80x94(CH)rxe2x80x94 or xe2x80x94CH2xe2x80x94C6H4xe2x80x94CH2xe2x80x94,
r represents an integer between 1 and 6,
Xxe2x88x92 represents a colourless anion which is redox-inert under the conditions,
where the bond to the bridge B is via one of the radicals R2-R11 or, if E1 or E2 represents NR1, is via R1, and the abovementioned radicals in that case represent a direct bond,
RED1 represents a radical of the formula (X), (XI), (XII), (XIII), (XVI), (XVII), (XVIII) or (XX),
where
R28 to R31, R34, R35, R38, R39, R46, R53 and R54 independently of one another denote C1- to C12-alkyl, C2- to C8-alkenyl, C5- to C7-cycloalkyl, C7- to C15-aralkyl or C6- to C10-aryl and
R46, R53 and R54 additionally denote hydrogen,
R32, R33, R36, R37, R40, R41, R47 to R52, R55 and R56 independently of one another denote hydrogen, methyl, ethyl, methoxy, ethoxy, fluoro, chloro, bromo, cyano, nitro, methoxycarbonyl, ethoxycarbonyl or phenyl, and
R57 and R58 additionally denote 2- or 4-pyridyl, and
R48 additionally denotes NR57R76,
Z3 denotes a direct bond, a xe2x80x94CHxe2x95x90CHxe2x80x94 or xe2x80x94Nxe2x95x90Nxe2x80x94 bridge,
xe2x95x90Z4xe2x95x90 denotes a direct double bond, a xe2x95x90CHxe2x80x94CHxe2x95x90 or xe2x95x90Nxe2x80x94Nxe2x95x90 bridge,
E3 to E5, E10 and E11, independently of one another denote O, S, NR59 or C(CH3)2, but E3 and E4 have the same meaning,
E6 to E9 are identical to one another and denote S, Se or N59, and
E5 additionally denotes Cxe2x95x90O,
E6 represents NR59, where R59 denotes a direct bond to the bridge B, and
E7 to E9 possess the meaning indicated above, but need not be identical to one another,
R59, R75 and R76 independently of one another denote C1- to C12-alkyl, C2- to C8-alkenyl, C5- to C7-cycloalkyl, C7- to C15-aralkyl or C6- to C10-aryl, and R75 additionally denotes hydrogen, or
R75 and R76 in the definition NR75R76 denote, together with the N atom to which they are attached, pyrrolidino, piperidino or morpholino,
R61, R62 and R67, R68 independently of one another represent hydrogen, C1- to C4-alkyl, methoxycarbonyl, ethoxycarbonyl or phenyl, or in pairs together represent a xe2x80x94(CH2)3xe2x80x94 or xe2x80x94(CH2)4xe2x80x94 bridge,
R63 to R66 represent hydrogen, and
v represents an integer from 1 to 6,
where the bond to the bridge B is via one of the radicals R28-R41, R46-R56, R61, R62, R67, R68 or, if one of the radicals E3-E11 represents NR59, is via R59, and the abovementioned radicals in that case represent a direct bond,
B represents a bridge of the formulae xe2x80x94(CH2)nxe2x80x94, xe2x80x94(CH2)mxe2x80x94Oxe2x80x94(CH2)pxe2x80x94, xe2x80x94(CH)mxe2x80x94NR60xe2x80x94(CH2)pxe2x80x94, xe2x80x94(CH2)mxe2x80x94C6H4xe2x80x94(CH2)pxe2x80x94, xe2x80x94[Oxe2x80x94(CH2)p]oxe2x80x94Oxe2x80x94, xe2x80x94[NR60xe2x80x94(CH2)p]oxe2x80x94NR60xe2x80x94, xe2x80x94[C6H4xe2x80x94(CH2)p]oxe2x80x94C6H4xe2x80x94, xe2x80x94(CH2)mxe2x80x94OCOxe2x80x94C6H4xe2x80x94COOxe2x80x94(CH2)pxe2x80x94, xe2x80x94(CH2)mxe2x80x94NHCOxe2x80x94C6H4xe2x80x94CONHxe2x80x94(CH2)pxe2x80x94, xe2x80x94(CH2)mxe2x80x94NHCONHxe2x80x94C6H4xe2x80x94NHCONHxe2x80x94(CH2)pxe2x80x94, xe2x80x94(CH2)mxe2x80x94OCOxe2x80x94(CH2)txe2x80x94COOxe2x80x94(CH2)xe2x80x94, xe2x80x94(CH2)mxe2x80x94NHCOxe2x80x94(CH2)txe2x80x94CONHxe2x80x94(CH)pxe2x80x94, xe2x80x94(CH2)mxe2x80x94NHCONHxe2x80x94(CH2)txe2x80x94NHCONHxe2x80x94(CH2)pxe2x80x94,
R60 represents methyl, ethyl, benzyl or phenyl,
n represents an integer from 1 to 10,
m and p independently of one another represent an integer from 0 to 4,
o represents an integer from 0 to 2, and
t represents an integer from 1 to 6,
and at least one UV absorber selected from the formulae (C), (CI) and (CII)
in which
R101 represents linear or branched C1- to C20-alkyl,
R102 represents hydrogen or cyano,
R103, R104 and R106 independently of one another represent hydrogen or C1- to C12-alkoxy,
R105 represents C1- to C12-alkoxy or hydroxyl,
R107 and R108 represent hydrogen or
R107 together with R108 represent xe2x80x94(CH2)2xe2x80x94, xe2x80x94(CH2)3xe2x80x94 or xe2x80x94CH2xe2x80x94C(CH3)2xe2x80x94, and
n and m independently of one another represent 1 or 2.
Special preference is given to an electrochromic solution of the invention which comprises at least one substance of the formula (Ia)-(Id)
in which
OX2 represents a radical of the formula (II), (IV) or (V)
in which
R2, R4 and R8 represent a direct bond to the bridge B,
R3, R5 and R9 independently of one another represent methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, benzyl or phenyl, or in the case of the formula Ic or Id likewise represent a direct bond to the bridge B,
R6 and R7 are identical and represent hydrogen, methyl, methoxy, chloro, cyano or methoxycarbonyl,
R10, R11; R12, R13 and R14, R15 independently of one another represent hydrogen or, if Z1 denotes a direct bond, represent, in each case in pairs together, a xe2x80x94CHxe2x95x90CHxe2x80x94 bridge,
R69 to R72 are identical and denote hydrogen, methyl or ethyl,
R73 and R74 denote hydrogen,
E1 and E2 are identical and represent O or S,
Z1 represents a direct bond or xe2x80x94CHxe2x95x90CHxe2x80x94,
Xxe2x88x92 represents a colourless anion which is redox-inert under the conditions,
RED1 represents a radical of the formula (X), (XII), (XIII), (XVI) or (XVII),
R28, R34, R38, R46 and R49 represent a direct bond to the bridge B,
R29 to R31, R35 and R39 independently of one another represent methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, benzyl or phenyl, or, in the case of the formula Ib or Id, R30, R35 and R39 likewise represent the direct bond to the bridge B,
R32 , R47 and R48 represent hydrogen,
R36, R37, R40, R41 and R50 to R52 independently of one another represent hydrogen, methyl, methoxy, chloro, cyano, methoxycarbonyl or phenyl, or, in the case of the formula Ib or Id, R51 likewise represents a direct bond to the bridge B,
Z3 represents a direct bond, a xe2x80x94CHxe2x95x90CHxe2x80x94 or xe2x80x94Nxe2x95x90Nxe2x80x94 bridge,
xe2x95x90Z4xe2x95x90 represents a direct double bond, a xe2x95x90CHxe2x80x94CHxe2x95x90 or xe2x95x90Nxe2x80x94Nxe2x95x90 bridge,
E3 to E5 independently of one another represent O, S or NR59, but E3 and E4 have the same meaning,
E6 to E9 are identical to one another and represent S, Se or R59,
R59 represents methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, benzyl or phenyl, or, in the case of the formula XVI in Ib or Id, likewise represents a direct bond to the bridge B,
B represents a bridge of the formulae xe2x80x94(CH2)nxe2x80x94, xe2x80x94(CH2)mxe2x80x94Oxe2x80x94(CH2)pxe2x80x94, xe2x80x94(CH2)mxe2x80x94NR60xe2x80x94(CH2)pxe2x80x94, xe2x80x94(CH2)mxe2x80x94C6H4xe2x80x94(CH2)pxe2x80x94, xe2x80x94Oxe2x80x94(CH2)pxe2x80x94Oxe2x80x94, xe2x80x94NR60xe2x80x94(CH2)pxe2x80x94NR60xe2x80x94, xe2x80x94(CH2)mxe2x80x94OCOxe2x80x94C6H4xe2x80x94COOxe2x80x94(CH2)pxe2x80x94, xe2x80x94(CH2)mxe2x80x94NHCOxe2x80x94C6H4xe2x80x94CONHxe2x80x94(CH2)pxe2x80x94, xe2x80x94(CH2)mxe2x80x94NHCONHxe2x80x94C6H4xe2x80x94NHCONHxe2x80x94(CH2)pxe2x80x94, xe2x80x94(CH2)mxe2x80x94OCOxe2x80x94(CH2)txe2x80x94COOxe2x80x94(CH2)pxe2x80x94, xe2x80x94(CH2)mxe2x80x94NHCOxe2x80x94(CH2)txe2x80x94CONHxe2x80x94(CH2)pxe2x80x94, xe2x80x94(CH2)mxe2x80x94NHCONHxe2x80x94(CH2)txe2x80x94NHCONHxe2x80x94(CH2)pxe2x80x94,
R60 represents methyl,
n represents an integer from 1 to 10,
m and p are identical and represent an integer from 0 to 2, and
t represents an integer from 1 to 6,
and at least one UV absorber selected from the formulae (C), (CI) and (CII)
in which
R101 represents methyl, ethyl, 1- or 2-propyl, 1- or 2-butyl, 1-hexyl, 2-ethyl-1-hexyl, 1-octyl or 1-dodecyl,
R102 represents hydrogen or cyano,
R103, R104 and R106 independently of one another represent hydrogen, methoxy, ethoxy, propoxy, butoxy, hexoxy or octoxy, and
R105 represents methoxy, ethoxy, propoxy, butoxy, hexoxy, octoxy or hydroxyl,
R107 and R108 represent hydrogen or
R107 together with R108 represent xe2x80x94CH2xe2x80x94C(CH3)2xe2x80x94, and
n and m independently of one another represent 1 or 2.
Very particular preference is given to an electrochromic solution of the invention which comprises at least one substance of the formula (Ia) corresponding to one of the formulae 
or at least one substance of the formula (Ic) corresponding to one of the formulae 
in which
R3, R5, R35 and R39 independently of one another represent methyl, ethyl, propyl, butyl, pentyl, hexyl or benzyl,
R6, R7 and R36, R37 in pairs are identical and represent hydrogen, methyl, methoxy, chloro, cyano or methoxycarbonyl,
R12 and R13 represent hydrogen or, if Z1 denotes a direct bond, together represent a xe2x80x94CHxe2x95x90CHxe2x80x94 bridge,
R69 to R72 are identical and represent hydrogen or methyl,
E1 and E2 are identical and represent O or S,
Z1 represents a direct bond or xe2x80x94CHxe2x95x90CHxe2x80x94,
R32, R47 and R48 represent hydrogen,
E3 to E5 independently of one another represent O, S or NR59, but E3 and E4 are identical,
R29 to R31 and R59 independently of one another represent methyl, ethyl, propyl, butyl, pentyl, hexyl or benzyl, with R29 to R31 preferably being identical,
R40 and R41 are identical and represent hydrogen, methyl, ethyl, propyl, butyl or phenyl,
Z3 represents a direct bond, xe2x80x94CHxe2x95x90CHxe2x80x94 or xe2x80x94Nxe2x95x90Nxe2x80x94,
R50 to R52 independently of one another represent hydrogen, methyl, methoxy, chloro, cyano, methoxycarbonyl, ethoxycarbonyl or phenyl, but are preferably identical,
E6 to E9 are identical to one another and represent S, Se or NR59,
Z4 represents a direct double bond, a xe2x95x90CHxe2x80x94CHxe2x95x90 or xe2x95x90Nxe2x80x94Nxe2x95x90 bridge,
m represents an integer from 1 to 5,
u represents 0 or 1, and
Xxe2x88x92 represents a colourless anion which is redox-inert under the conditions,
and a UV absorber of the formula (C)
in which
R101 represents ethyl or 2-ethyl-1-hexyl,
R102 represents hydrogen,
R103 represents ethoxy or methoxy in m- and/or p-position,
R107 and R108 represent hydrogen or
R107 together with R108 represent xe2x80x94CH2xe2x80x94C(CH3)2xe2x80x94, and
n and m independently of one another represent 1 or 2,
or a UV absorber of the formula (CI)
in which
R101 represents ethyl or 2-ethyl-1-hexyl,
R102 represents cyano, and
R103 and R104 represent hydrogen and
n and m represent 1,
or a UV absorber of the formula (CII)
in which
R105 represents methoxy, ethoxy, octoxy or hydroxyl, and
R106 represents hydrogen,
or a mixture of the UV absorbers of the formulae (C) and (CI) or a mixture of the UV absorbers (C) and (CII) or a mixture of the UV absorbers (CI) and (CII) or a mixture of the UV absorbers (C) and (CI) and (CII),
in which the radicals possess the meaning indicated above.
Very particular preference is given to an electrochromic solution of the invention which comprises a UV absorber of the formula 
or a UV absorber of the formula 
or a UV absorber of the formula 
or a UV absorber of the formula 
or a mixture of the UV absorbers of the formulae (CIII) and (CIV) or a mixture of the UV absorbers of the formulae (CIV) and (CV) or a mixture of the UV absorbers of the formulae (CIII) and (CV) or a mixture of the UV absorbeer of the formulae (CIIIa) and (CIV) or a mixture of the UV absorber of the formulae (CIIIa) and (CV).
The substances of the formula (I) are known from WO 97/30134.
In the abovementioned definitions of substituents alkyl radicals, including modified versions such as alkoxy or aralkyl radicals, for example, are preferably those having 1 to 12 C atoms, especially having 1 to 8 C atoms, unless indicated otherwise. They can be straight-chain or branched and can if desired carry further substituents such as, for example, C1- to C4-alkoxy, fluoro, chloro, hydroxyl, cyano, C1- to C4-alkoxycarbonyl or COOH.
Cycloalkyl radicals are preferably those having 3 to 7 C atoms, especially 5 or 6 C atoms.
Alkenyl radicals are preferably those having 2 to 8 C atoms, especially 2 to 4 C atoms.
Aryl radicals, including those in aralkyl radicals, are preferably phenyl or naphthyl radicals, especially phenyl radicals. They can be substituted by 1 to 3 of the following radicals: C1- to C6-alkyl, C1- to C6-alkoxy, fluoro, chloro, bromo, cyano, hydroxyl, C1- to C6-alkoxycarbonyl or nitro. Two adjacent radicals can also form a ring.
The electrochromic solution of the invention comprises at least one solvent. Suitable solvents are all solvents which are redox-inert at the chosen voltages and which cannot give off electrophiles or nucleophiles or themselves react as sufficiently strong electrophiles or nucleophiles and so could react with the coloured ionic free radicals. Examples are propylene carbonate, xcex3-butyrolactone, acetonitrile, propionitrile, glutaronitrile, methylglutaronitrile, 3,3xe2x80x2-oxydipropionitrile, hydroxypropionitriile, dimethylformamide, N-methylpyrrolidone, sulpholane, 3-methylsulpholane or mixtures thereof. Preference is given to propylene carbonate and to mixtures thereof with glutaronitrile or 3-methylsulpholane.
The electrochromic solution of the invention can include at least one inert conductive salt.
Suitable inert conductive salts are lithium, sodium and tetraalkylammonium salts, especially the latter. The alkyl groups can have between 1 and 18 C atoms and can be identical or different. Tetrabutylammonium is preferred.
Suitable anions for these salts, and also those anions Xxe2x88x92 in the formulae (I), (II), (IV), (VI) and (VII) are all colourless anions which are redox-inert. Examples are tetrafluoroborate, tetraphenylborate, cyano-triphenylborate, perchlorate, chloride, nitrate, sulphate, phosphate, methanesulphonate, ethanesulphonate, tetradecanesulphonate, pentadecanesulphonate, trifluoromethanesulphonate, perfluorobutanesulphonate, perfluorooctanesulphonate, benzenesulphonate, chlorobenzenesulphonate, toluenesulphonate, butylbenzenesulphonate, tert-butylbenzenesulphonate, dodecylbenzenesulphonate, naphthalenesulphonate, biphenylsulphonate, benzenedisulphonate, naphthalenedisulphonate, biphenyldisulphonate, nitrobenzenesulphonate, dichlorobenzenesulphonate, trifluoromethylbenzenesulphonate, hexafluorophosphate, hexafluoroarsenate, hexafluorosilicate, 7,8- or 7,9-dicarba-nido-undecaborate(1-) or (2-), each of which is unsubstituted or substituted on the B and/or C atoms by one or two methyl, ethyl, butyl or phenyl groups, and also dodecahydro-dicarbadodecaborate(2-) or B-methyl-C-phenyl-dodecahydro-dicarbadodecaborate(1-). In the case of polyvalent anions Xxe2x88x92 represents one equivalent of this anion, e.g. 1/2 SiF62xe2x88x92.
Preferred anions are tetrafluoroborate, pentadecanesulphonate, dodecylbenzenesulphonate, cyanotriphenylborate and 7,8-dicarba-nido-undecaborate(1-).
The conductive salts are preferably employed in the range from 0 to 1 molar.
Further possible additives to the electrochromic solution are thickeners, in order to control the viscosity of the fluid. This can be important for avoiding segregation, i.e. the formation of stripey or spotty coloration on prolonged operation of an electrochromic device comprising the electrochromic fluid of the invention, in the switched-on state, and for controlling the rate of fade after switching off the current.
Suitable thickeners are all compounds usual for these purposes, such as polyacrylate, polymethacrylate (Luctite L(copyright)), polycarbonate and polyurethane, for example.
The electrochromic solution can also be in gel form.
A constituent of the electrochromic solution of the invention comprises, in accordance with the invention, UV absorbers. They are employed in the range from 0.01 to 2 mol/l, preferably from 0.04 to 1 mol/l. The UV absorbers present in the solution of the invention are known in principle or can be prepared in analogy to the preparation of known UV absorbers. Preferred UV absorbers are those of the formulae (CIII) (e.g. UVINUL(copyright) 3088, BASF), (CIV) (e.g. UVINUL(copyright) 3039, BASF) and (CV) (e.g. CHIMASSORB(copyright) 90, Ciba). These products are highly soluble in the stated solvents: for example, at least 0.8 molar in propylene carbonate.
The action of the UV absorber was measured in electrochromic cells as described below. The exposure apparatus used was the Xenotest 150 S from Heraeus. The output was 1570 W/m2 in the xe2x80x9coutdoor sunlightxe2x80x9d configuration.
It was found, surprisingly, that mixtures of these UV absorbers are considerably more effective than the individual substances. For example, a mixture of the UV absorbers of the formulae (CIV) and (CV) in concentrations of 0.05 molar each is just as effective as the UV absorber of the formula (CIV) alone in a concentration of 0.4 molar.
The electrochromic solution of the invention comprises the substances of the formula (I), especially of the formulae (Ia) to (Id), in each case in a concentration of at least 10xe2x88x924 mol/l, preferably from 0.001 to 1 mol/l. It is also possible to employ mixtures of two or more electrochromic substances of the formula (I).
The electrochromic solutions of the invention are eminently suitable as a constituent of an electrochromic device. In an electrochromic device the electrochromic solution of the invention serves as variable-transmission medium, in other words, under the influence of an electrical voltage the light transmittance of the solution changes, and it passes from a colourless to a coloured state. A further subject of the present invention, accordingly, are electrochromic devices comprising an electrochromic solution of the invention. The design of an electrochromic device, which may be configured, for example, as a window pane, car sunroof, car rearview mirror or display, is known in principle. The electrochromic device of the invention consists of two facing, transparent glass or plastic plates of which one may be mirrored and whose facing sides carry an electroconductive coating of, for example, indium tin oxide (ITO) and between which there is located the electrochromic fluid of the invention. Other suitable conductive materials are antimony-doped tin oxide, fluorine-doped tin oxide, antimony-doped zinc oxide, aluminium-doped zinc oxide, tin oxide; and also conductive organic polymers, such as unsubstituted or substituted polythienyls, polypyrroles, polyanilines, polyacetylene. If one of the plates is mirrored, it can also be used as a conductive layer. The distance between the two plates is generally 0.005-2 mm, preferably 0.02-0.5 mm. The desired distance between the plates is generally established by means of a sealing ring.
Such cells were also used to determine the action of the UV absorbers (see above).
In the case where the electrochromic device is an electrochromic display device, at least one of the two conductive layers, or both, are subdivided into electrically separate segments that are contacted individually.
Alternatively, it is possible for only one of the two plates to carry the conductive coating and to be subdivided into segments. The separation of the segments can be effected, for example, by means of mechanical removal of the conductive layer, for example by scoring, scratching, scraping or milling, or chemically, for example by etching using, for instance, a solution of FeCl2 and SnCl2 in hydrochloric acid. This removal of the conductive layer can be locally controlled by means of masks, for example photoresistant masks. Also possible, however, is the production of the electrically separate segments by means of controlledxe2x80x94for example, by means of masksxe2x80x94applicationxe2x80x94for example, sputtering or printingxe2x80x94of the conductive layer. The contacting of the segments takes place, for example, by means of fine strips of conductive material, by means of which the segment is brought into electrically conducting communication with a contact at the edge of the electrochromic device. These fine contact strips can consist either of the same material as the conductive layer itself and can be prepared, for example, along with said layer at the same time as it is subdivided into segments as described above. Alternatively, in order to improve the conductivity, they can consist of a different material, such as fine metallic conductors made, for example, from copper or silver. A combination of metallic material and the material of the conductive coating is a further possibility. These metallic conductors may, for example, be applied, e.g. bonded, in fine wire form, or else may be printed on. All of these above-described techniques are common knowledge from the production of liquid-crystal displays (LCD).
The displays can be viewed in transmitted light or else reflectively via mirror coating.
The two plates are laid atop one another with the conductively coated and segmented sides facing, separated by means, for example, of a sealing ring, and are bonded to one another at the edge. The sealing ring may be made, for example, of plastic or thin glass or another material which is inert with respect to the electrochromic fluid. The distance between the plates can also, however, be established by means of different spacers, for example by means of small plastic or glass beads or particular fractions of sand, in which case these spacers are applied together with the adhesive and then together form the sealing ring. The sealing ring includes one or two cutouts which are used to fill the electrochromic device. The distance between the two plates ties between 0.005 and 2 mm, and is preferably from 0.02 to 0.5 mm. In the case of large-surface-area display devices, especially those made of plastic, it may be advantageous to use spacers, for example plastic beads of equal diameter distributed over the area of the display device, to keep the distance between the plates constant.
This display device is filled with an electrochromic fluid via the apertures in the sealing ring, an operation which must be carried out at all times with exclusion of moisture and oxygen. Filling can be carried out, for example, by means of fine cannulas or else by the vacuum filling technique, in which the device and the fluid are placed into a shallow dish and introduced into an evacuable container. This container is evacuated. Then the display device, which includes only one filling aperture, is dipped with said aperture into the fluid. When the vacuum is removed, the fluid is then forced into the display device.
The self-erasing single-cell electrochromic device of the invention can in addition to the above-described electrochromic substances of the formulae (I), especially of the formulae (Ia) to (Id), also include other such substances, as are described, for example, in U.S. Pat. No. 4,902,108, Topics in Current Chemistry, Vol. 92, pp. 1-44 (1980) and Angew. Chem. 90, 927 (1978). Such electrochromic substances hail, for example, from the groups indicated above, under the formulae (II) to (XX), in which case none of the radicals listed is able to possess the definition xe2x80x9cdirect bond to the bridge Bxe2x80x9d. Examples of other suitable electrochromic co-components are tetrazolinium salts or salts or complexes of metal ions, e.g. [Fe(C5H5)2]0/1+. The admixture of such redox systems may, for example, be advantageous in order to correct the colour of the electrochromic device of the invention, for example of the display, in the switched-on state or to render the said colour more intense.